Projection systems in use today are often used to project the images displayed on a computer screen, onto a larger display screen. The ability of projection systems to project images displayed on a computer screen onto a larger display screen has proven particularly useful when presenting to an audience, as it allows each audience member to better view an image on the computer screen.
It is known to use projection systems in place of computer screens. These projection systems usually connect directly to a computer hard drive and project a Graphical User Interface onto a display screen (as opposed to the Graphical User Interface being displayed on a computer screen).
Projections systems which project virtual devices are also known. For example projections systems which project the image of a keyboard are known. Such projection systems may further comprise a detector which is operable to detect the position fingers within a frame of the projected image of the keyboard. The detector can detect at which key the user has positioned a finger thereby providing a virtual keyboard.
By using a projection system which projects a virtual keyboard along with a projection system which can project the Graphical User Interface of a computer onto a display screen, a virtual computer is provided. However, to achieve a virtual computer, two distinct projection systems are required, a first projection system to project a virtual keyboard onto a display surface and a second projection system is required to project the Graphical User Interface onto a display screen. The hardware required to achieve a virtual computer is thus expensive and is far too large for integration in mobile devices.
To reduce the cost of the hardware required for the projection of a virtual computer, it is known to use a single projector to project two images successively; the projector projects a first image e.g. a virtual keyboard onto a first display screen, after the projection system has completed projection of the virtual keyboard, it subsequently projects a second image e.g. the Graphical User Interface of a computer, onto a second display screen. The speed at which the first and second images are projected is such that both images are simultaneously visible to a user. To project the first and second images onto the first and second display screens respectively, the projection system comprises a single reflective surface which oscillates about oscillation axes to scan light across the display screens.
In the case of the projection with a single or dual MEMS scanning system, the light comprises pulses, each pulse of light corresponding to a pixel of an image. The reflective surface is oscillated about a first oscillation axis to scan light in a zig-zag or lissajou pattern across the first display screen to display the first image pixel-by-pixel, the reflective surface is then displaced and oscillated about a second oscillation axis to scan light in a zig-zag or lissajou pattern across the second display screen to display the second image pixel-by-pixel. In the case of the projection with a DLP (Digital Light Processing), LCOS (Liquid Crystal On Silicon) or LCD (Liquid Crystal Display) type-based projection systems, the light from the first image is deflected by an oscillating reflective surface then followed by the redirection of the light of the second projected image.
It is required that each of the first and second images be refreshed at a minimum threshold frequency so that complete images it will be visible on each of the first and second display screens; so once the reflective surface has oscillated to scan light across the second display screen to display the second image, the reflective surface returns to scan light across the first display screen to display the first image once more; this process is continuously repeated and is done at a speed which ensures that the first and second images appear to a viewer to be simultaneously projected onto their respective display screens. The reflective surface is required to oscillate at a minimum speed to ensure that both the first and second images are refreshed at the minimum threshold frequency (normally at a frequency which is greater than the human eye persistence); so that, to a viewer, complete first and second images are simultaneously visible on the first and second display screens respectively.
As the two images are projected in succession, it is necessary for the reflective surface to oscillate twice as fast, compared to a reflective surface in a projector which projects a single image, so that both of the projected images are refreshed at the minimum threshold frequency. If the first and second images are not refreshed at the minimum threshold frequency (or a frequency which is greater than the minimum threshold frequency) the image qualities of the first and second images would be compromised, and complete first and second images would not be simultaneously visible to a viewer on the respective display screens. The high speed of oscillation of the reflective surface, required to ensure that both of the projected images are refreshed at the minimum threshold frequency (or greater), is difficult to attain and demands high power consumption.
It is an aim of the present invention to obviate or mitigate one or more of the aforementioned disadvantages.